Physics (Internal)

Quantum Impurity Physics with Microwave Photons

This event is part of the Condensed Matter Theory Seminar Series.

Abstract: We consider the propagation of microwave photons along an array of superconducting grains with a set of weakly-coupled grains at its center. Quantum fluctuations of the charge on the weakly-coupled grains make the process of "photon splitting" effective. In such a process, an incoming photon may be split into a number of photons of lower energy. The minimal number of photons so created depends on the symmetry properties of the corresponding quantum impurity model. As an example, we consider a specific circuit allowing quantum fluctuations between two charge configurations of two weakly-coupled grains, thus mimicking the behavior of an anisotropic Kondo impurity. We relate the total rate of conversion of incoming photons into lower-energy ones to the linear dynamic spin susceptibility of the Kondo model. The spectral distribution of the outgoing photons yields information about higher-order local correlations in the quantum impurity dynamics. Finally, we reveal a relation between this problem and transport along the edge of a 2D topological insulator coupled to a magnetic impurity.